Method for rendering microcellular staple fibers self-inflatable in air involving the continuous transporting of the fibers through a reaction pipeline

ABSTRACT

A PROCESS IS PROVIDED FOR RENDERING MICROCELLULAR STAPLE FIBERS SELF-INFLATABLE IN AIR. THE FIBERS ARE SUBMERGED, BECOME ENTANGLED TO FORM CLUMPS, OR SLUGS, AND PASS THROUGH TREATMENT PIPES IN &#34;SLUG FLOW&#34; WHERE THEY ARE CONTACTED WITH TREATMENT LIQUIDS. ALL FIBERS HAVE SUBSTANTIALLY THE SAME RESIDENCE TIME IN THE TREATMENT LIQUIDS. THE TREATMENT LIQUIDS COMPRISE: (1) &#34;PLASTICIZING&#34; LIQUIDS, WHICH PLASTICIZE THE CELL WALLS TO PERMIT FLUIDS TO DIFFUSE INTO THE CELLS, (2) &#34;BOOSTING&#34; LIQUIDS, COMPRISING IMPERMEANT INFLATANTS WHICH DIFFUSE INTO THE CELLS WHILE THE WALLS ARE PLASTICIZED, BUT NORMALLY DO NOT PERMEATE THE CELLS WHEN THE WALLS AR NOT PLASTICIZED, AND (3) &#34;STRIPPING&#34; LIQUIDS, WHICH REMOVE PLASTICIZING LIQUID, DEPLASTICIZE THE CELL WALLS AND TRAP IMPERMEANT INFLATANT WITHIN THE CELLS. FIBERS SO TREATED WHEN EXPOSED TO AIR BECOME FULLY INFLATED.

July 3, 1973 M. "r. CICHELLI ET AL 3,743,694 METHOD FOR RENDERINGMICROCEL ULAR STAPLE FIBERS SELF-INFLATABLE IN AIR INVOLVING THECONTINUOUS TRANSPORTING OF THE FIBERS THROUGH A REACTION PIPELINE FiledJuly 13, 1971 4 Sheets-Sheet 1 F::i 2| (IN?! N) m l 7- I 1 l 1 m o- I lm a I ATTORNEY 1 July 3 973 M.T. CICHELLI ETAL 3,743,694

METHOD FOR RENDERING MICROCELULAR STAPLE FIBERS SELF-INFLATABLE IN AIRINVOLVING THE CONTINUOUS TRANSPORTING OF THE FIBER THROUGH A REACTIONPIPELINE Filed July 13, 1971 4 Sheets-Sheet 2 IOI INVENTORS MARIO THOMASCICHELLI DAVID ROSS COLLEY ARTHUR IILLIAI ETCHELLS. III WILLIAM JAMESSHIT ATTORNEY July 3, 1973 M. T. CICHELLI ET AL 3,743,694 METHOD FORRENDERING MICROCEL ULAR STAPLE FIBERS SELF-INFLATABLE IN AIR INVOLVINGTHE CONTINUOUS TRANSPORTING OF THE FIBERS THROUGH A REACTION PIPELINE 4Sheets-Sheet 3 Filed July 13, 1971 INVENTORS M Est v N s m IL .I L n L E.L "I A lmv q GE I. PVILIS u A SHMflu s TR I RA ul mwflul. V L A R IDA YB July 3, 1973 M. T. CICHELLI ET AL 3,743,694 METHOD FOR RENDERINGMICROCEL ULAR STAPLE FIBERS SELF- INFLATABLE 1N AIR INVOLVING THECONTINUOUS TRANSPOHTING OF THE FIBERS THROUGH A REACTION PIPELINE 4Sheets-Sheet 4 Filed July 13, 1971 ARTHUR IILLIAI ETCHELLS. III II LIANJAIE SIITH ATTORNEY United States Patent 4 Claims ABSTRACT OF THEDISCLOSURE A process is provided for rendering microcellular staplefibers self-inflatable in air. The fibers are submerged, becomeentangled to form clumps, or slugs, and pass through treatment pipes inslug flow where they are contacted with treatment liquids. All fibershave substantially the same residence time in the treatment liquids. Thetreatment liquids comprise: (1) plasticizing liquids, which plasticizethe cell walls to permit fluids to diffuse into the cells, (2) boostingliquids, comprising impermeant infiatants which diffuse into the cellswhile the walls are plasticized, but normally do not permeate the cellswhen the walls are not plasticized, and (3) stripping liquids, whichremove plasticizing liquid, deplasticize the cell walls and trapimpermeant inflatant within the cells. [Fibers so treated when exposedto air become fully inflated.

REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of application Serial No. 738,522, filed June 20,1968, now abandoned. 1

BACKGROUND OF THE INVENTION (1) Field of the invention This inventionrelates to buoyant, closed-cell polymeric, foamed, staple fibers,sometimes referred to as microcellular fibers, and more particularly toa method and apparatus for transporting such fibers in slug flow whilesubmerged in a special treatment liquid. More specifically, theinvention relates to a pipeline process for postinflating such fibers,and to apparatus for carrying out this process.

(2) The prior art Foamed polymeric materials are widely used forcushioning applications. Generally they fall into three classifications:(1) those of elastomeric polymers, e.g., rubber and certainpolyurethanes, which derive their cushioning properties primarily fromelasticity of the copolymer; (2) those of relatively rigid polymerstructure which tend to provide good impact energy absorption withoutresilient regain of initial dimensions; (3) and those of thin-walledclosed-cell foamed polymer which confine gases within the closed cellsand are pneumatically resilient. This invention is concerned with foamedfibers, or microcellular fibers, of the latter type, particularly staplefibers which are collected and adhesively bonded at fiber-to-fibercontacts to yield cushioning batts.

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Known gas-inflated closed-cell foams have had, in general, certaindeficiencies. Ordinarily they are air-inflated. Rarely, however, is airthe gas originally contained within the cells immediately afterclosed-cell foamformation, the original gases having usually permeatedout of the cell-walls rapidly. Thus, exposure to air results in anexchange of gases until air becomes the sole gas contained. Depending onthe relative permeation rates for air and for the gas originallypresent, the period during which gas-exchange occurs ordinarily ischaracterized by dimensional changes in the product, very often bypartial or complete collapse of the cells of the foam. The gas pressurewithin the cells at equilibrium with ambient air cannot exceedatmospheric pressure, and, if collapse occurs during gas-exchange, thereremains no spontaneous mechanism for reinfiating the cells to theirmaximum volumes established when the polymer in the cell wallssolidified during foam expansion.

For cushioning applications, however, a more serious deficiencycharacterizes customary pneumatic foams, even if they are prepared infully inflated form. Air is composed of small, rapidly permeatingmolecules. While transient compressive loads may result in little or noloss of air, repeated or sustained compressions eventually cause most orall of the air to escape by permeation. Once air is lost in thisfashion, it is not spontaneously regained, and pneumatic resilience ispermanently diminished or destroyed.

British Pat. No. 1,062,086, published Mar. 15, 1967, discloses a processwhereby the above disadvantages of pneumatic, closed-cell foams areovercome. According to this process, an impermeant inflatant isintroduced within the closed cells to inflate them. The impermeantinflatant is a normally gaseous material of relatively large molecularsize and is chemically inert toward and substantially completelyinsoluble in the polymer comprising the foam. Examples of impermeantinflatants include sulfur hexafiuoride and saturated aliphatic andcycloaliphatic compounds having at least one fluorine-to-carbon covalentbond and wherein the number of fluorine atoms exceeds the number ofcarbon atoms, such as perfluorocyclobutame and chloropentafluoroethane.

The impermeant infiatants permeate the cell walls so slowly as to besubstantially permanently retained within the foam cells-regardless ofthe number, frequency, or duration of the compressive loadings. Thepresence of impermeant inflatant within foam cells creates an osmoticgradient for the inward permeation of air. At equilibrium with theambient atmosphere, the internal partial pressure for air becomessubstantially atmospheric. This, combined with the partial pressure forimpermeant inflatant, provides a superatmospheric total internalpressure and guarantees full reinflation of the closed cells. Moreover,even if some air is lost during compressive loading, impermeantinflatant remains and causes spontaneous regain of both volume andpneumaticity of the foam structure when the load is removed.

One method for introducing impermeant inflatant to the closed cells ofthe foam is to incorporate the impermeant inflatant in the foamablecomposition prior to its extrusion to form foam fibers. However, thefoamed fibers are preferably postinflated in place of or in addition tothe introduction of impermeant inflatant directly by extrusion.

Postinflation is the name applied to the overall process in whichpreviously formed foam, either collapsed or gas-inflated, is: (1)exposed to impermeant inflatant while the cell walls are plasticized andtemporarily of greatly enhanced permeability; (2) treated to quicklystrip off the plasticizing agent by vaporization; and (3) equilibratedin air (preferably heated) until the foam at least regains its maximumvolume. Further exposure to air might increase the internal gaspressures somewhat, but it should produce substantially no furthervolume increase.

Step (1) above can be accelerated somewhat by subjecting the foamimmersed in impermeant inflatant treatment fluid to elevated pressures,but it is difiicult to handle large volumes of continuously formed foamstaple in such a process. A continuous, substantially atmosphericpressure process is preferable. Although the treatment fluids may beeither gaseous or liquid, liquid-phase treatment is preferred.

In a previously employed atmospheric postinflation process, as disclosedin Bonner, U.S. Pat. 3,381,077, the foamed, closed-cell, polymeric,staple fibers are continuously conveyed on or between reticulateconveyor belts as beds of fiber, being drawn sequentially through threeclosed vessels where they are either immersed in or showered by theliquid phases contained therein. The first vessel contains aplasticizing liquid preferably heated to its normal atmospheric boilingpoint. The second contains a substantially saturated solution ofimpermeant inflatant in plasticizing liquid which is called a boosterliquid. This booster liquid is also usually maintained at substantiallythe normal atmospheric boiling point of the mixture. The third containsa stripping liquid such as water (or other similarly inert fluid) at asufiiciently elevated temperature to quickly vaporize substantially allof the residual plasticizing fluid and the superficial impermeantinflatant. In this manner, plasticization of the cell walls is sosuddenly terminated that impermeant inflatant becomes trapped within theclosed cells of the foam fibers. The vapors are simultaneously withdrawnto appropriate solvent-recovery means. Thereafter, postinflation iscompleted by exposing the fibers to heated air at a temperature belowthe melting or flowing temperature for the polymer, e.g., usually at 70to 175 C. Liquid/vapor seals are, of course, provided at both entranceand exit of each vessel.

Alternatively, and as also disclosed in Bonner U.S. Pat. 3,381,077, theplasticizing and the inflating of the fibers (carried out in theforegoing paragraph in the first and second vessels, respectively) maybe combined and may be carried out simultaneously.

While the above procedures are workable on a continuous basis, acontinuous procedure has heretofore had several disadvantages. It is somechanically complex, with myriad drive and supporting rolls, thatmechanical failure is frequent. This tendency is severely aggravated bythe necessity for exposing a majority of the moving parts to corrosivevapors and liquids. Finally, liquid/ vapor seals between vessels largeenough to accommodate beds of fibers are iuefiicient; consequently, theload on and expense of solvent-recovery are rather great.

SUMMARY OF THE INVENTION This invention provides an improvement in theprocess for treating microcellular staple fibers at substantiallyatmospheric pressure to render them postinflatable upon exposure to airby contacting the fibers with a 1) plasticizing liquid, (2) a liquidcontaining an impermeant inflatant (sometimes referred to as a boostingliquid), and (3) a stripping liquid. Liquids (1) and (2) can becombined, if desired. The improvement comprises continuouslytransporting the fibers through a reaction pipeline with such treatingliquid in slug flow at a rate of one to two feet per second.

The fibers used in this invention tend to collect into coherent,interentangled clumps (or slugs) as they are submerged in the liquid andbegin to move through the pipe-length; hence, the expression slug flow.Since no individual fiber can proceed through the pipe slower or fasterthan the clump (or slug) it is in, obtainment of slug flow assures thatall fibers will receive about equal treatment times in the treatingliquid as they move through the pipe. Obtainment of slug flow is the keyto usefulness of this invention since it enables treatment of thebuoyant fibers to take place in the absence of the complex mechanicalequipment described previously. It is surprising and unexpected thatslug flow is attained because of the turbulent flow conditions thatexist as the fibers and treating liquid pass through the pipe (0.5 to 5feet per second and preferably 1 to 2 feet per second) and because ofthe buoyancy of the fibers (a density between 0.005 and 0.1 gm./cc.).

The invention also provides the utilization of apparatus for carryingout the above-described process which comprises a generally horizontalpipe-length, means at the entrance end of the pipe-length for submergingthe fibers in the treatment liquid and introducing the fibers and liquidto the pipe-length, means in the pipe-length for providing suflicienthead to the liquid to move the fibers and liquid through the pipe-lengthwith the fibers in slug flow, and means at the exit end of thepipe-length for separating the fibers from the liquid.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representationin elevation of an improved postinflation process and apparatus providedby this invention.

FIG. 2 is an enlarged, schematic, cross-sectional view in elevation ofapparatus suitable for the plasticizing section I of FIG. 1.

FIG. 3 is a similar view showing the boosting section II of FIG. 1.

FIG. 4 is a similar view showing the stripping section III of FIG. 1.

DESCRIPTION OF THE INVENTION The invention is an improvement in theprocess of postinflating microcellular staple fibers, i.e., fibers thatare buoyant, polymeric, closed-cell, foamed staple fibers. Both thesemicrocellular fibers and processes for inflating them are known in theart. The fibers are made of a foamed polymer having discrete polyhedralshaped closed cells defined by cell walls less than two microns inthickness, with substantially all of the polymer being present in thecell walls. As described in U.S. Pat. 3,227,664 and 3,381,- 077, thesemicrocellular fibers contain at least 10 cells/ cc., the averagetransverse dimension of the cells is ordinarily less than about 1000microns in the expanded state, and the cell walls exhibit uniplanarorientation and uniform texture. The fibers, when in a collapsed state,have densities usually in the range from 0.05 to 0.1 gm./cc.; but whenfully inflated their densities are in the range from 0.016 to 0.030gm./cc., and their diameters are from about 0.03 to 0.10 inch. Thelength of the staple fibers is from about 1.5 to 8 inches. Preferably,the fibers are made of polyethylene terephthalate prepared as describedin the aforesaid U.S. patents.

The microcellular staple fibers in the collapsed state can bepostinflated (called postinflated to distinguish from inflationoccurring during the spinning of the fibers) by exposing them toimpermeant inflatant while the cell walls are plasticized andtemporarily of greatly enhanced permeability. The impermeant inflatantpermeates the cell walls easily due to the plasticized state of theWalls, but when the walls are not plasticized, the impermeant inflatantpermeates the cell walls so slowly as to be substantially permanentlyretained Within the cells. Thus, after exposure to the inflatant thefibers are treated to quickly strip off the plasticizing agent byvaporization. The presence of the inflatant within the walls creates anosmotic gradient for permeation of air in the cells. Thus, on exposureto air, an equilibrium is established wherein the partial pressure ofair in the cells becomes essentially atmospheric. This combined with thepartial pressure of the inflatant, produces a superatmospheric pressurewithin the cells, thereby inflating them. In their inflated state, thefibers are very light weight and highly buoyant, and this pneumaticitymakes the fibers highly suited for use in cushioning structures.

As described above, previous art processes for postinflating the fibersemployed conveyor belts and required mechanical handling in transportingthem from one conveyor belt to another. In the present invention, it hasbeen discovered that even though the microcellular fibers are of lowdensity, and therefore buoyant, they can be submerged in the treatmentliquids and transported through pipes by means of a state termed slugflow. The term slug flow as used herein describes the tendency of themicrocellular fibers to collect and become entangled in clumps, or slugsas the fibers are submerged in the treatment liquid and moved throughthe pipe. Because of the velocity and turbulence of the treatmentliquids moving through the pipe, it is surprising that the light,microcellular staple fibers are able to form clumps or slugs. Since thefibers travel in slugs, the residence time of each individual fiber inthe pipes is about the same, i.e., the individual fibers do not travelat different velocities and do not pass one another, or the like. Veryfew individual fibers pass through the pipeline independently. When theconcentration of the fibers in the treatment liquid is low, smalldiscrete clumps of fiber form, separated by relatively long sections ofclear treatment liquid in the pipeline. When the fiber concentration issomewhat higher, but still relatively low, somewhat larger size clumps,approaching the size of tennis balls, can form. These too aretransported by the treatment liquid in slug flow through the pipeline asdiscrete clumps separated by sections of clear treatment liquid. Atstill higher concentrations of fiber in the treatment liquid, the formedclumps can approach three to four feet in length. These too pass throughthe pipeline as discrete clumps in slug flow but are separated byshorter sections of clear treatment liquid. Further increases in fiberconcentration can cause an essentially continuous clump to form and betransported by the liquid through the pipeline. As the concentration offiber increases, the size of the clumps increases and the distance oftravel in the pipeline before clumps start to grow decreases. However,for all these described conditions, the residence times of all fibersare substantially identical since no fiber can proceed through the pipeslower or faster than the slug it is in.

Although the reason for the formation of clumps or slugs is notcompletely understood, it is believed to be due at least in part to theunique surface characteristics of the microcellular staple fibers.

Suitable microcellular fibers for use in this invention are preparedfrom synthetic crystallizable, organic polymers, and as described in US.Pat. 3,227,664, include poly hydrocarbons such as linear polyethylene,stereo-regular polypropylene or polystyrene; polyethers such aspolyformaldehyde; vinyl polymers such as polyvinylidene fluoride;polyamides both aliphatic and aromatic, such as polyhexamethyleneadipamide and polymetaphenylene adipamide and polymetaphenyleneisophthalarnide; polyurethanes, both aliphatic and aromatic, such as thepolymer from ethylene bischloroformate and ethylene diamine; polyesterssuch as polyhydroxypivalic acid and polyethylene terephthalate;copolymers such as polyethylene terephthalate-isophthalate, and thelike. The polymers are of at least film forming molecular weight.

As described in US. Pat. 3,381,077, suitable plasticizing liquids foruse in the process of this invention should have relatively smallmolecules in order to promote permeation through the cell walls and mustplasticize (e.g., swell) the cell walls without dissolving other thanvery minor proportions of the polymer and at below the fluidsatmospheric boiling point. At high temperatures,

and under pressure, most suitable plasticizing liquids dissolve at leasta significant portion of the polymer. Since it must be readily andrapidly volatized on exposure to air, the plasticizing liquid shouldhave an atmospheric boiling point of less than about C. The rate ofplasticization increases with increasing temperature; so operation earits boiling point is preferred. Prolonged exposure to plasticizingliquid can change the crystalline structure and molecular orientation ofthe polymer in the cell-walls, usually increasing their permeability; sothe shortest adequate plasticizing times are employed, usually in therange from 5 to 60 seconds. Thus, the term plasticizing liquid as usedherein means a volatile, low boiling liquid substance that isessentially a non-solvent for the polymer employed at or below theboiling point of the fluid, but has sufficient solvent power to swell,i.e., plasticize, the fiber polymer. Suitable plasticizing liquids forfoamed fibers of polyethylene terephthalate include methylene chloride,chloroform, ethylene chloride, and dichlorofluoromethane. Methylenechloride with a boiling point of about 41 C. is preferred not onlybecause it is optimum in the above properties but also because it isrelatively inexpensive, nontoxic except in extreme exposures, andsubstantially nonflammable.

The term impermeant inflatant as used herein means a gas or liquid oflow boiling point which permeates the cell walls of the unplasticizedmicrocellular staple fibers so slowly, as compared to air, that it issubstantially permanently retained within the closed cells, even undercompression, but which readily permeates the cell walls of theplasticized fibers, and which has a large molecular size as isconsistent with a vapor pressure of at least 50 mm. of mercury at normalroom temperature. As described in US. Pat. 3,381,077, suitableimpermeant inflatants are selected from the group consisting of sulfurhexafluoride and saturated aliphatic or cycloaliphatic compounds havingat least one fluorine-to-carbon covalent bond and wherein the number offluorine atoms preferably exceeds the number of carbon atoms. Preferablythese inflatants are perhaloalkanes or perhalocycloalkanes in which atleast 50% of the halogen atoms are fluorine. Although these inflatantsmay contain ether-oxygen linkages, they are preferably free fromnitrogen atoms, carbon-to-carbon double bonds, and reactive functionalgroups. Specific examples of impermeant inflatants include sulfurhexafluoride, perfluorocyclobutane, symdichlorotetrafiuoroethane,chloropentafluoroethane, perfiuoro 1,3-dimethylcyclobutane,perfluorodimethylcyclobutane mixtures, 1,1,2-trichlor0 1,2,2trifluoroethane, CF CF CF OCFHCF chlorotrifluoromethane, anddichlorodifluoromethane. Particularly preferred because of itsinertness, appreciable molecular size, very low permeability rate, andlack of toxicity is perfluorocyclobutane with an atmospheric boilingpoint of about 6 C., especially when the microcellular fibers areprepared from polyethylene terephthalate.

The term stripping liquid as used herein means a liquid at normalconditions that is a nonsolvent for the microcellular fibers andnonreactive with the impermeant inflatant and the plasticizing fluid.The function of the stripping liquid is to aid in physically strippingexcess inflatant and plasticizer from the fibers. A wide range ofliquids may be employed, however, water is preferred.

The process of this invention, i.e., the transporting of the buoyantmicrocellular staple fibers through the pipeline in slug flow, can becarried out with the three stage sequence disclosed in US. Pat.3,381,077, i.e., the treatment of the fibers sequentially (1) in aplasticizing liquid to temporarily increase the permeability of the cellwalls; (2) in a boosting liquid comprising impermeant inflatant tointroduce impermeant inflatant into the closed cells; and (3) in astripping liquid substantially inert to and insoluble in both thepolymer and previous treatment liquids to vaporize and remove excessexternal impermeant inflatant and substantially all the residualplasticizing liquid and to trap -the remaining impermeant inflatantwithin the cells. Alternatively, the process may be carried out by thetwo stage sequence disclosed in co-assigned copending United Statespatent application Ser. No. 162,281, filed concurrently herewith, whereno separate plasticizing step is used, but rather both the plasticizingand boosting functions are provided by a treatment liquid consisting ofa dilute dispersion or solution of plasticizer and impermeant inflatantin water.

In the three-stage procedure, the process of this invention is carriedout continuously by submerging the fibers first in the plasticizingliquid and moving the fibers and plasticizing liquid through a firstpipe-length in slug flow, separating the fibers from the plasticizingliquid, submerging the fibers in the boosting liquid and moving thefibers and boosting liquid through a second pipe-length in slug flow,separating the fibers from the boosting liquid, submerging the fibers inthe stripping liquid and moving the fibers in slug flow and strippingliquid through a third pipe-length, and separating the fibers from thestripping liquid. In the two-stage procedure, the process of thisinvention is carried out by submerging the fibers in the aqueousdispersion or solution of the plasticizing and boosting liquids, andtransporting them in slug flow through a pipeline of sufficient lengthto permit the cell walls to become plasticized and the impermeantinflatant to enter the cells. The fibers are then separated from thisfirst treatment liquid, submerged in a stripping liquid, moved in slugflow with the stripping liquid through a second pipe-length and thenseparated from the stripping liquid. The resultant fibers areself-inflatable in air.

The invention also provides an apparatus for performing the slug flowprocess which comprises three successively coupled pipe-lengths, meansat the entrance end of each pipe-length for submerging the fibers in atreatment liquid and introducing the fibers and liquid to thepipe-length, means in each pipe-length for moving the liquid and fibersthrough the pipe-length with fibers in slug flow, means at the exit endof each of the first two pipe-lengths for continuously separating thefibers from the bulk of the treatment liquid and transferring the fibersto the submerging means of the next pipe-length, means at the exit endof the third pipe-length for continuously separating the fibers from thebulk of the treatment liquid and transferring them to a holdup tank. Ofcourse, in the two-step procedure only two successively coupledpipelengths are needed.

The slug flow process will now be described with respect to thethree-step postinfiation procedure of the prior art and with respect tothe drawings (in which the various parts are designated by the samenumerals throughout).

PLASTICIZING SECTION With reference to FIGS. 1 and 2, the plasticizingsection is designated by the Roman numeral I. Microcellular foamedstaple fibers 8 are continuously supplied to a collection vessel 10.Vessel 10 is usually vented via line 103 to a condenser (not shown) forliquefying vapors of plasticizing-fluid and for maintainingsubstantially atmospheric pressure. A generally horizontal pipe-length16 has a vertical submerging section and turns upward at its other endto join coupling tank '14. Respective liquid levels for plasticizingliquid in these two portions are indicated by numerals 1 and 2. As thevery low-density fibers 8 approach liquid level 1, they are submerged bya stream of plasticizing liquid from lines 18 and 18'. Liquid liquideductor 11 moves the fibers and liquid through pipelength 16 to couplingtank 14. In generating sufiicient pressure to forward the fibers andliquid, eductor 11 introduces an excess of plasticizing liquid.Consequently, a regulator 13 is provided which is simply a shellsurrounding a portion of pipe-length 16. Within regulator 13, pipelength16 has openings 9 sized to allow liquid but not fibers 8 to flowthrough. In this way, excess plasticizing liquid is drawn from regulator13 by circulating pump 12.

8 Fibers 8 are moved through pipe-length 16 in slug flow. On reachingthe end of pipe-length 16, fibers 8 float to the liquid surface 2, wherethey contact cooperating, rotating, squeeze-rolls 17. A screen-enclosedchannel 19, larger in cross-section than is pipe-length 16, allows readyflow therethrough of plasticizing liquid while preventing the strayingof fibers 8.

Squeeze-rolls 17 form a seal between section I and II by forcing excessplasticizing liquid back into coupling tank 14. Simultaneously theyforward fibers 8 via connecting bafile 20, on to section II. Frequently,jets (not shown) of boosting liquid are employed to assist in transferof fibers 8 through bafile 20. Suitable squeeze-rolls may have eithercompressible or rigid surfaces, the latter preferably provided withshallow ridges to aid in catching fibers 8. Squeeze-rolls 17 cooperatewith surrounding surfaces 20' to form a seal against loss of treatmentfluid and ordinarily have diameters approximately equal to the diameterof pipe-length 16 where it enters coupling tank 14, and equal lengthssufiiciently greater than said diameter that transport of all fibersfloating to the nip is assured.

Liquid recirculation is provided by circulating pump 12 which withdrawsliquid from pipe-length 16 via regulator 13 and from coupling tank 14via pipe 102. Simultaneously, liquid is forced into pipe-length 16 viaeductor 11 and through pipe 18 for fiber submersion.

It is apparent that suitable controls must be provided for thisplasticizing section and that a variety of types of controls can providethe desired balance of flow-rates. In a. preferred control system,automatic valves controlled by sensing (alternatively sensing andrecording) devices are employed. Thus, liquid-level sensing device 104-controls flow of plasticizing liquid at 101 through valve 105 tomaintain liquid-level 2. Dual flow-rate sensors 106 and 107 provide acombined signal for withdrawal of liquid from regulator 13 via automaticvalve 108. The rate of injection of plasticizing liquid into eductor 11via automatic valve 110 is controlled by pressure sensor 109 upstreamfrom eductor 11. Finally, flow-rate sensor 111 controls the flow ofsubmerging liquid through automatic valve 112. Though not indicated inFIGS. 1 and 2, all exposed surfaces of apparatus should be thermallyinsulated, and heaters 115 must be provided at one or more points tokeep the plasticizing fluid, preferably methylene chloride, at itsboiling point.

BOOSTING SECTION With reference to FIGS. 1 and 3, the boosting sectionis designated by Roman numeral II. In this section, the fibers 8 areexposed to impermeant inflatant while plasticization of the cell wallsis maintained. Thus, the boosting liquid is usually a solution ofimpermeant inflatant in the plasticizing liquid.

Operation of this section is substantially equivalent to that forsection I. Pipe-length 26 for this treament is rather great, asindicated by its serpentine shape in the figures. It is, however,preferably in a generally horizontal plane over most of its length. Dueto its length and to the consequently large friction losses, ahigh-capacity pump 21 is ordinarily preferred to an eductor. However, alarge liquid/liquid eductor can be employed alternative y.

Fibers 8 conducted from section I via baffle 20 are submerged at liquidlevel 3 by flow of booster liquid from pipes 28 and 28, this flow-ratebeing controlled by flowrate sensor 209 in combination with automaticvalve 210. The fiber-slurry is drawn down the vertical submerging pipe25 and into pipe-length 26 by slurry pump 21. As in section I, aregulator 23 is provided from which submerging liquid is withdrawn bycirculating pump 22 and from which further liquid can be recycledthrough valve 207. The speed of pump 22, and thereby its capacity, iscontrolled by pressure-sensor 108. Treated fibers 8 float up throughcoupling tank 24 to liquid level 4 where squeezerolls 27 withdraw fibers8 and forward them to section III via baffle 30. Seals 30 preventpassage of liquids. Booster liquid is recycled from tank 24 to pump 21via pipe 213 at a rate detected by flow-rate sensor 211 and controlledby automatic valve 212.

A preferred liquid for a boosting section from which water is completelyexcluded in the azeotropic mixture of methylene chloride andperfluorocyclobutane. As long as at least 9.1% by weight of the mixtureis perfluorocyclobutane, it boils at 6 C. Two equilibrium liquid phasesdevelop, a methylene chloride-rich phase comprising about 9.1% by weightof perfluorocyclobutane and a perfluorocyclobutane-rich phase comprisingabout 88% by weight of perfluorocyclobutane. Sinse the lighter, lessexpensive methylene chloride-rich phase provides a thermodynamicactivity for perfluorocyclobutane identical to that of the other phase,the lighter phase is preferably circulated through pipe-length 26 atabout -6 C. If water is present in the boosting section, for example,because of inadequate sealing between the boosting section and thedownstream aqueous stripping section, boiling of the azeotropic mixtureat -6 C. leads to ice formation. Accordingly, when water is present, itis preferred to operate with a boosting liquid comprising a 1 to 5%solution of perfluorocyclobutane in methylene chloride at a temperaturebetween about 1 and 25 C. The details surrounding coupling tank 24 inFIGS. 1 and 3 reflect the use of the azeotropic mixture as boosterfluid. Liquid-level 4, the top of the lighter phase, is detected byliquid-level sensor 203 which controls automatic valve 204 for the inputof methylene chloride or booster fluid at 201. Liquid-level 5, the topof the denser phase, is detected by liquid-level sensor 205 whichcontrols automatic valve 206 for the input of perfluorocyclobutanerichliquid 202. Pipe 213 extends into lighter phase, and screen-enclosedchannel 29 has an impermeable section 29' extending to about level 5. Inaddition to a perfluorocyclobutane-rich stream at 202, it is alsodesirable ordinarily to inject some at 216 in order to preventexhaustion of perfluorocyclobutane in pipe-length 26.

As in section I, all exposed surfaces of apparatus should be thermallyinsulated. Cooling by heat transfer to a cooling medium, e.g.,refrigerated brine, must be provided at one or more points. A jackettype heat-exchanger 215 in the circulation loop is particularlydesirable because the fibers entering through baflle 20 are hot andcarry superficial hot methylene chloride.

A booster liquid comprising methylene chloride andchloropentafluoroethane is similarly preferred when no water is presentin the boosting section. It, too, is preferably cooled to about -6 C.,but it does not form an azeotropic mixture. If it is used, controls 205and 206 are replaced with concentration-detection devices forcontrolling input of chloropentafluoroethane at 202 and at 216.

STRIPPING SECTION FIGS. 1 and 4 depict the preferred stripping section,indicated by Roman numeral HI. The purposes of the stripping section areto remove plasticizing and excess boosting liquids, deplasticizing thecell walls and trap the inflatant within the closed cells. Operation andconstruction of this section are substantially as described for sectionI except that hot water is the preferred stripping liquid and that amanifold 311 for removing released vapors is provided.

Staple fibers 8 arriving via bafiie 30 are submerged below water level 6by flow of water from pipes 38 and 38'. Vapors (generated by theplasticizing and boosting liquids from the preceding pipeline sections)above water level 6 are removed and sent to solvent recovery via line214 (FIG. 1). Flow-rate sensor 208 detects water flow-rate and controlsit through automatic valve 309. Water flow is induced by circulatingpump 32, which discharges most of the water via valve 307 to liquid/liquid eductor 31. Water enters pump 32 via pipe 312 from coupling tank34 and via valve 306 from regulator 33. Flow-rate sensors 304 and 305control automatic valve 306. Coupling tank 34 has water-level 7 which ismaintained by sensor 302 and automatic valve 303. As before,screen-enclosed channel 39 leads the fibers 8 up to the nip with rollers37. Heaters 315 are provided at one or more points in the strippingsection to maintain the water temperature.

Regulator 33 differs from the regulators 13 and 23 in that it enclosesmost of pipe-length 36 and provides not only for liquid-flow regulationbut also for the removal of vaporized plasticizing liquid and impermeantinflatant. Bubbles of this vapor rise through stand-pipes of manifold311, above liquid levels 310, and on to solvent recovery means (notshown) as indicated by arrow 301. The eflicient removal of vaporsthrough pipe-length 36 within regulator 33 requires a high degree ofopenness in the pipe-wall. Well-screen piping is preferred for thatsection of pipe-length 36 within regulator 33. Bafiles 313 are providedbetween the well-screen piping and the wall of regulator 33 to preventthe liquid from passing through the well-screen and by-passing thefibers, which would result in the fibers being held up in pipe-length36. If desired, a pipe connecting the last section of regulator 33 withreturn pipe 312 can be provided to permit withdrawal of some clearliquid and to diminish the quantity of liquid being separated from thefibers through screen 39 in coupling tank 40. A hand operated valve inthis pipe provides adequate control.

Pipes 18, 28', and 38' are positioned so as to introduce liquid alongthe inner wall of the upper conical portion of the respective verticalsubmerging pipes 15, 2S and 35 in a manner which will impart a downwardspiraling motion to the liquid. The purpose is to centrifuge out gasbubbles. The gas bubbles and fibers are of similar densities. Thus,velocity suflicient to submerge the fibers will also submerge the gasbubbles. However, with the swirling motion of the liquid, the fibers,due to their length, are pulled down the sides of the vertical pipes,whereas the gas bubbles are centrifuged to the center and escape. Aportion of the liquid in each section is introduced through pipe 18, 28or 38 and permitted to flow down as a centrally directed stream,preferably a spray. This is particularly important in the plasticizationsection (FIG. 2) where dry staple is to be submerged.

Following stripping, fibers 8 are dried in air. For polyethyleneterephthalate fibers, air temperatures from 70 C. to 175 C. are foundeffective. Heated air is passed at high velocity across the outlet fromrollers 37, as indicated by arrow 41. Some purge of vapor-laden air via42 is provided. Retention of the fibers in hold-up tank 40 at 70 C. to175 C. (preferably about C.) for 1 to 30 minutes, varying inversely withthe air temperature employed, causes air reinflation of the fibers. Itis apparent that continuous conveyance of the fibers through an air ovencan replace hold-up tank 40. It is unnecessary to complete the inflationof dried fibers at this point, and subsequent re-exposure to heated airto establish approximate osmotic equilibrium for air is often desirable.

OPERATING CONDITIONS AND DIMENSIONS fal where L is the length of thepipe,

T is the desired time of exposure to each liquid,

W is the flow rate for fibers expressed as weight of fibers per unit oftime,

A is cross-sectional area of the pipe,

d is density of the staple fibers,

S is the fraction of the total volume of pipe actually filled by flowingfibers, and

v is linear velocity of fibers in the pipe.

The units for variables used in Equation 1 must, of course, be selectedfrom one consistent system of units. For the postinflation of thepreferred polyethylene terephthalate ultramicrocellular staple,flow-rates (W) in the range of from about 100 to about 2500 pounds ofpolymer per hour (about 45 to about 1100 kg. of polymer per hour) are ofparticular interest. Density (d) of the staple during treatment isdetermined largely by the temperature of the treatment liquid. Thus, inthe heated plasticizing section I) and stripping section (III), thepreferred staple has a density (d) of the order of 1 lb./-ft. (0.02 gm./cc.); but in the cold boosting section (II), density (d) is of the orderof 3.0 to 4.5 1b./ft. (0.048 to 0.072 gm./cc.). Treatment times (T) varyfrom section to section. In the plasticizing section (I), residencetimes (T) of from to seconds are efiective. In the boosting section(II), from 1 to minutes is the range in which sufiicient impermeantinflatant is introduced within the closed cells. Adequate removal ofexcess solvents in stripping section (III) occurs ordinarily intreatment times of from 15 to seconds. Volume percentages (100-S) of thefibers in the pipes are ordinarily from 2 to 20% to provide slug flowwhile avoiding excessive frictional resistance to flow. With aconcentration of about 2% or greater, the fibers become entangled andform coherent slugs (or clumps) almost immediately upon introductioninto a pipe-length. Even with lower concentrations, say /2 volumepercent or less, the fibers collect to form clumps within a short time.

Thus, the only variables of Equation 1 which remain unspecified are L,A, and v. Although fiber-velocity (v) can vary over quite wide limits,values of from 1.0 to 2.0 ft./sec. are ordinarily preferred. From aknowledge of these variables, Equation 1 can be solved for suitablevalues of pipe-length (L) and cross-sectional area (A) of the pipe.Actually, an infinite set of A-L values results, but the range isnarrowed by the desirability that L be much greater than the transversecross-sectional size of the pipe. Also, cross-sectional areas (A) equalto those of circles with diameters from about 4 to 24 inches (10 to 60cm.) are found most suitable, increasing with increasing fiow rate (W).

EXAMPLE I Preferred ultr-amicrocellular fibers as hereinabove definedare continuously prepared by extrusion at a rate of about 100 lb./hr.kg./hr.) of polymer through 24 extrusion orifices. The uniform foamablecomposition is composed of about 65% polyethylene terephthalate and 35%methylene chloride (both percentages by weight). Temperature andpressure of this solution just prior to passage through the extrusionorifices are about 215 C. and about 650 p.s.i.g. (46 kg./cm. gauge),respectively. Each extrusion orifice is a cylindrical hole about 0.012inch (0.30 mm.) in diameter and about 0.006 inch (0.15 mm.) long. If theextruded fibers are collected directly in ambient air, the fiberscollapse to a density of the order of 0.1 gm./cc. or higher withinseconds, due both to condensation of methylene chloride within the cellsand to its rapid escape by diffusion. Thereafter, the fibers are notspontaneously reinfiatable and remain only slightly pneumatic.

In this example, the fibers are extruded into methylene chloride vaporin equilibrium with the boiling liquid (41 C.). Collapse is therebyprevented, the expanded fibers are cut to staple in this atmosphere, andthe staple is discharged at about 100 lb./hr. (45 kg./hr.) to collectionvessel 10 where they are immersed in boiling methylene chloride (41 C.)in submerging section 15 of pipe 16. Submerging pipe-length 15, leadingto eductor 11, is 4.0 inches (10.2 cm.) in inside diameter, and theremainder of pipe-length 16 is 6.0 inches (15.2 cm.) in inside diameter.Fiber velocity in pipe-length 16 is about 2.0 ft./sec. (0.61 m./sec.),and total residence time in boiling methylene chloride is about 15seconds. The corresponding liquid velocity is about 2.7 ft./sec. (0.82m./ sec.). Sufiicient liquid methylene chloride flows via pipe 18 toprovide a liquid velocity of about 3 ft./sec. (0.91 m./sec.) in the 4.0inch (10.2 cm.) diameter pipe. Eductor 11 and circulating pump 12 areselected to provide these velocities as well as a range of variabilityas hereinabove specified. Screen-enclosed channel 19 is square withabout 8.0 inch (20 cm.) sides. Squeeze-rolls 17 have compressibleelastomeric surfaces, are 6.0 inches (15.2 cm.) in diameter, and form anip about 0.5 inch (1.3 cm.) above liquid level 2.

Booster section (II) is operated as hereinbefore detailed. Again, thevertical submerging section is 4.0 inches (10.2 cm.) in inside diameter,and the remainder (nearly all) of pipe-length 26 is 6.0 inches (15.2cm.) in inside diameter. The liquid circulated is composed of about 9parts by weight of perfiuorocyclobutane and 91 parts of methylenechloride and is maintained at about 6 C. The staple resides in thisliquid about 15 minutes. In pipe-length 26, staple velocity is about 1.0ft./sec. (.30 m./sec.), and liquid velocity is about 1.3 ft./ sec. (0.40m./sec.). Liquid is introduced via pipe 28 sufficient to provide aliquid velocity in submerging section 25 of about 5.0 ft./sec. (1.52m./sec.). Sizes of screen-enclosed channel 29 and squeeze rolls 27 areidentical to those in section 'I.

In section III, the stripping fluid is Water maintained at about 70 C.Submerging pipe-length 35 is 6.0 inches (15 .2 cm.) in diameter, butpipe-length 36 following eductor 31 is oval in cross-section with 4' and12 inch (10.16 and 30.48 cm.) axes, the larger axis in the horizontalplane. Most of pipe-length 36 is well-known well-screen piping to allowescape of liberated gases to solvent recovery. Treatment time in wateris about 30 seconds at a fiber-velocity in the oval pipe of 1.0 ft./sec. (0.31 m./sec.) and a watervelocity of about 2.3 ft./sec. (0.70m./sec.). Water is injected via pipe 38 to provide a water-velocity inthe submerging section of about 3.0 ft./ sec. (0.91 m./sec.).Squeeze-rolls 37 are as previously described, but screenenclosed channel39 is increased to an 8 x 16 inch (20.3 x 40.6 cm.) rectangle in orderto enclose the exit of the oval pipe.

The staple is removed from the stripping section (III) in a stream ofhot air and is held in air at about C. for about 20 minutes. Thereafter,it becomes fully inflated, round in cross-section, and highly pneumatic.

'In a particularly preferred embodiment of the apparatus of thisinvention, the inner walls of the pipe-lengths are coated with alow-friction coating, e.g., polytetrafluoroethylene. This isparticularly advantageous for very long pipe-lengths such as arecharacteristic of the boosting section. Pressure drop which occurs onpumping closed-cell, foamed, staple fibers through such a coatedpipe-length is reduced to only one-quarter to one-half that required inan identical uncoated pipe-length. In the pumping of customary heavyslurries, e.g., sand, little or no pressure drop from interaction of theslurried solids with pipe-walls has been observed. Low-density foamedfibers, however, possess high surface friction, are urged by buoyancyagainst pipe-walls, and transmit frictional resistance-to-fiow at thewalls by fiber-entanglement to the whole flowing slug of fibers. Inorder to maintain a given flow rate of fibers, the liquid must be pumpedcorrespondingly faster to overcome the friction at the pipe-walls. Thus,low-friction coating of the inner walls of a pipe-length greatlydecreases the power required to maintain a given fiber-flow velocity.

EXAMPLE II In this example, microcellular staple fibers of polyethyleneterephthalate of the same type as used in Example I are postinflated insubstantially the same equipment as in Example I and under the sameconditions, with the following exceptions:

The fibers, which are treated in the above-described manner at a rate ofpounds per hour, are then heated in air at 125 C. for minutes. Thefibers are then cooled.

EXAMPLE 'III This example illustrates the use of the process andapparatus of this invention in treating buoyant staple fibers ofclosed-cell foamed organic polymer with a boosting fluid consisting of avery dilute concentration of plasticizer and impermeant inflatant inwater to render the fibers postinfiatable.

Ultrarnicrocellular staple fibers, spun and cut in accordance withExample I, are collected in bags and then hand fed at a rate of about 20pounds per hour to collection vessel 10 of FIG. 1, where they areimmersed in water at about 18 C., submerged in submerging section 15,forwarded to eductor 11 and then passed through pipelength 16 where thefibers travel at a velocity of about 2.6 to 2.7 ft./sec. and the watertravels at about 3.2 ft./sec. At the end of pipe-length 16, the fibersand water flow vertically into a fiber-liquid separating device. Thislatter device has a horizontal open-mesh screen onto which the fibersand water are dropped. The water passes through the screen and isrecycled. The fibers are forwarded on the screen through squeeze rollsand then are doifed from the screen by rapidly rotating brushes whichadvance the fibers to the vertical submerging portion of Section -II.Note that in this example, Section I is filled with water and is usedfor distributing and feeding fibers to booster section H (of FIG. 1) andfor preventing loss of organic vapors from section II. No plasticizingoccurs.

In booster section II of FIG. 1, the treatment (i.e., boosting) liquidcomprises at least about 97 weight percent water and small amounts ofplasticizer and impermeant inflatant. The liquid has two phases, asolution phase and a dispersed phase. The solution phase contains about2 weight percent methylene chloride plasticizer and very small amountsof perfiuorocyclobutane impermeant infiatant. The dispersed phasecontains 96 weight percent methylene chloride and 4 weight percentperfluorocyclobutane. At the inlet to booster section H, the treatmentliquid is 99 weight percent solution and 1 weight percent dispersedphase. At the outlet to booster section II, the concentration of thedispersed phase is reduced to 0.65 weight percent, due to the entry ofthe plasticizer and impermeant inflatant into the cells of the staplefibers. The temperature of the treatment liquid in the boosting sectionis maintained at 8 C. In 900-foot long, 6-inch Schedule 10 pipe-length26, the fiber velocity is about 1.0 ft./sec., and the boosting liquidvelocity is about 1.5 ft./sec. The fibers, which pass through theboosting section entangled in discrete clumps (i.e., in slug flow), havea residence time in boosting section II of about 15 minutes. The liquidvelocity is submerging section is about 1.5 ft./sec. Fibers areseparated from the boosting liquid at the end of the boosting section bya device which consists of a rotating open mesh cylindrical screen onwhich the fibers are dropped and through which the liquid passes forrecirculation. After passage through a squeezeroll nip, the fibers aredotted from the screen by means of rapidly rotating brushes and advancedto the vertical submergence pipe-length 35 of stripping section III.

In section HI, the treatment liquid (i.e., stripping liquid) is watermaintained at about 63 C. The fibers are submerged in 6-inch, SchedulelO-pipe-length 35 and forwarded by eductor 31 to pipe-length 36 which inthis Example is a 8-inch, Schedule 10 pipe, the upper 120 degress ofwhich is well-screen piping to allow escape of perfluorocyclobutane andmethylene chloride vapors to solvent recovery. Treatment time in thestripping section is about 15 seconds. The fibers flow through the pipeentangled in discrete clumps at a velocity of about 2 ft./ sec. Thewater velocity is about 4.7 ft./sec. Liquid velocity in the submergencesection at the entrance to the strip ping section is about 2.5 ft./sec.A fiber-liquid separator of the type coupled to Section I removes thefibers from the stripping section. At this point at least about 8 gramsof impermeant infiatant (i.e., perfluorocyclobutane with essentially nomethylene chloride) per 100 grams of fiber polymer are contained withinthe closed cells of the fibers.

The fibers removed from the stripping section are then forwarded to abin through which hot air at -125 C. is passed for between 20 and 60minutes. The fibers are then cooled.

As a result of the treatment given the fibers in this example, thefibers become fully inflated, turgid, round in cross-section and highlypneumatic.

While dimension, controls, conditions, etc., given hereinabove arespecific to two preferred systems, the description is believedadequately detailed to enable one skilled in the art to readily adaptthe invention to other systems and other applications. As manyalternatives and alternations are apparent without departing from thescope of this invention, it is not intended to be limited by theforegoing details.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In the substantially atmospheric-pressure process for treatingbuoyant, closed-cell, foamed, microcellular staple fibers prepared fromsynthetic crystallizable organic polymers to render them postinfiatableupon exposure to air, which process comprises contacting the fibers withtreating liquids, said treating liquids comprising either (a) aplasticizing liquid that swells the cell 'walls of the fiber but isessentially a nonsolvent for the polymer of the fiber, liquid containingan impermeant infiatant that is sulfur hexafluoride or a saturatedaliphatic or cycloaliphatic compound having at least onefluorine-to-carbon covalent bond and wherein the number of fluorineatoms exceeds the number of carbon atoms, and stripping liquid that is anonsolvent for the fibers and nonreactive with the impermeant infiatantand the plasticizing liquid, employed in sequence, or (b) saidplasticizing liquid and said liquid containing impermeant inflatantemployed simultaneously, followed by said stripping liquid, theimprovement which comprises:

submerging the fibers sequentially in each aforedescribed treatingliquid and transporting said fibers with said liquid or mixture thereofin slug flow through a pipeline at a rate of about 0.5 to about 5 feetper second and at a fiber volume such that the fibers occupy from one totwenty percent of any given cross-section of the pipeline.

2. The process improvement of claim 1 wherein the fibers are sub-mergedand moved through one pipeline with the plasticizing liquid, separatedfrom the liquid, submerged and moved through a second pipeline with theliquid containing an impermeant inflatant, separated from said liquid,and submerged and moved through another pipeline with the strippingliquid.

3. The process improvement of claim 1 wherein the fibers are submergedand moved through one pipeline with a mixture of the plasticizing liquidand the impermeant inflatant, separated from the mixture, and submergedand moved through another pipeline with the stripping liquid. 3,587,2576/ 1971 Hurter 16219 X 4. The process improvement of claim 2 wherein the2,944,292 7/1960 Norrhede 26451 X fibers are prepared from polyethyleneterephthalate, the 3,227,664 1/ 1966 Blades 264-41 X plasticizing liquidis methylene chloride, the impermeant 3,344,221 9/ 1967 Moody 264-321inflatant is selected from the class consisting of perfiu- 5orocyclobutane and chloropentafluoroethane, and the FOREIGN T PStripping liquid is Waten 1,062,086 3/1967 Great Britain.

R f s Ci PHILIP E. ANDERSON, Primary Examiner UNITED STATES PATENTS 10CL 2,493,740 1/1950 Adams 8156 2,431,478 11/1947 Hill X 8 68 117 161170, 260 25 R,

3,381,077 4/1968 Bonner, Jr. 264321 N; 264 53 13

